General Motors expects its Chevrolet Cruze to remain a force in the small-car segment, despite declining sales figures in recent months as its Asian rivals rebuild inventories and all-new midsize cars with similar fuel economy hit the market.

Cruze sales last month tumbled 20.3% to 19,613 units from 22,711 year-ago. The downturn represents one of the few blemishes for GM in an otherwise strong May, where deliveries on a daily-selling-rate basis rose 2.4%, according to WardsAuto data.

The industry saw two extra selling days in May of this year compared with like-2011. It was GM’s best May in four years and its highest monthly sales since August 2009, the restructured auto maker says.

The Cruze serves as a cornerstone of a newly profitable small-car machine underpinning GM’s turnaround from its 2009 bankruptcy and growing the U.S. share of its largest division, Chevrolet.

Last year the Cruze spent four months as the No.1 seller in the WardsAuto Upper Small segment. But its reign coincided with production snafus on the Ford Focus and the depleted availability of traditional segment leaders, the Toyota Corolla and Honda Civic, due to the disasters in Japan. Since February, the Cruze has fallen to fourth place in its segment.

Now the Japanese auto makers are building to capacity again and the segment as a whole could see pressure from all-new midsize cars with improved fuel economy hitting the market later this year, as Ford’s chief sales analyst suggested yesterday.

“We’re pretty happy with what we’re doing with (the) Cruze right now,” Don Johnson, GM’s top sales analyst tells WardsAuto in a conference call to discuss the auto maker’s May sales earlier today.

Johnson agrees the competitive landscape will change over the coming months, and predicts GM will gain strength in the small-car segment with the recent addition of the Sonic B-car and Spark subcompact later this year.

In the midsize segment, GM currently offers a redesigned Chevy Malibu Eco, and this fall the nameplate will receive two more fuel-sipping variants.

“We look at it across all segments,” Johnson says, noting GM has kept Cruze incentives flat while competitors are discounting more aggressively.

“Based on what we’ve seen and what our forecast is, we’re pretty comfortable,” Johnson says, admitting Cruze sales likely will fluctuate this year by “a few hundred units” each month. “But overall, we feel pretty good about the walk we have in the (Chevy) showroom from a pricing, incentive and features standpoint.”

GM expects to maintain a 3-shift operation at the Cruze’s Lordstown, OH, assembly plant despite the changing competitive environment. “No production changes planned,” Johnson says.

GM’s new Chevy Malibu Eco launched earlier this year accounted for 1,600 units of the nameplate’s 29,579 deliveries last month, up 6.7% year-over-year. The auto maker expects the mild-hybrid model to hold about a 20% share of Malibu sales after the two traditional powertrains arrive.

Overall, Chevy deliveries rose 1.8% to 177,943 units, with the Traverse, Equinox, Silverado and Tahoe all posting gains.

Cadillac continued feeling pressure from its sparse showroom, with sales tumbling 21.2% to 9,871 units. However, the new XTS large car starts arriving at dealers this week, and the ATS small sport sedan, which will occupy luxury’s highest-volume segment, comes later this summer.

“It’s a very exciting time in the history of Cadillac,” Johnson says, noting the division later this year will have entries in all of luxury’s best-selling segments for the first time in many years.

Buick sales rebounded in May, up 10% to 18,565 units, driven by a 43.3% surge in deliveries of the Enclave large CUV. GMC sales grew 10.1%.

GM reiterates its forecast for 2012 industry light-vehicle sales of between 14.0 million and 14.5 million units on an annualized basis.